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Temperature‐Dependent Behavior of the Dual Fluorescence of 2‐(3‐Fluorophenyl)‐2,3‐dihydro‐1 H ‐benzo[ f ]isoindole‐1,3‐dione
Author(s) -
Valat Pierre,
Wintgens Véronique,
Kossanyi Jean,
Biczòk Làszlò,
Demeter Attila,
Bérces Tibor
Publication year - 2001
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20010919)84:9<2813::aid-hlca2813>3.0.co;2-7
Subject(s) - chemistry , excited state , solvent , quantum yield , activation energy , cyclohexane , photochemistry , atmospheric temperature range , solvent effects , diethyl ether , analytical chemistry (journal) , fluorescence , organic chemistry , thermodynamics , physics , quantum mechanics , nuclear physics
The fluorescence behavior of 2‐(3‐fluorophenyl)‐2,3‐dihydro‐1 H ‐benzo[ f ]isoindole‐1,3‐dione ( 1 ) was studied in solvents of different polarity and viscosity. Dual luminescence is observed and the short‐wavelength emission is found to increase considerably with the solvent polarity. The ratio of the fluorescence quantum yield of the two states emitting, the one (SW*) at short wavelength and the other (LW*) at long wavelength, shows a bell‐shaped dependence on the reciprocal of the temperature in diethyl ether, butyronitrile, and propane‐1,2,3‐triol triacetate (glycerol triacetate; GTA). This has been interpreted as the result of a reversible interconversion between the two states. The enthalpy difference between the SW* and LW* excited states, as deduced from the slope of the ln ( Φ / Φ ) vs. 1/ T curves in the high temperature range, is found to be solvent polarity and solvent viscosity independent as the same value (−7.3 kJ/mol) is obtained in the three above‐mentioned solvents. The independence from polarity is the consequence of a similar difference in dipole moment between the ground‐state and the SW* and LW* excited states (4.5 and 4.9 D, respectively, derived from solvatochromy). The activation energy of the SW*→LW* step deduced from the low temperature measurements in the nonviscous solvents, increases with solvent polarity (11.6 and 17.5 kJ/mol for diethyl ether and butyronitrile, respectively); they are greater than the viscous‐flow activation energy of the solvents indicating that the resolvation of the excited dipole controls the kinetics. In the nonviscous solvents, the LW* state originates from the SW* state, while in the viscous GTA solution, both states are formed simultaneously within the 1‐ps laser pulse.